Today we celebrate the transcendental surd pi, because today is 14 March, which in America is spelled out 3.14, which happen to be the first three digits of pi, aka π, which is that Greek letter you had to know in high school.

Pi is important past high school: it’s the ratio of a circle’s circumference to its diameter, and – before your eyes glaze over – humanity wouldn’t have come very far without its help in everything from engineering to physics to art.

(I gave up on math way back in high school, so I apologize to fanatics for stinting on detail. Alex Bellos likes numbers much more than I do; he can help you. I’m here for the lay folk.)

Anyway, besides its uses, what’s interesting about pi is that it’s an irrational number, aka a “surd”, which is more fun to say. Irrationals are real numbers that can’t be expressed as a ratio. In practical terms, it’s a decimal that’s neither finite (like 2.0 or 1.24) nor repeating (like 1.3333) nor periodic (like 9.1818). It just keeps going past 3.14159 for as long as you’d like to take it, and because humanity has had loads of spare time to kill, people have taken it out to 2,700 billion decimal places (Count von Count of Sesame Street is also on the case).

In other words, pi is “infinite” … in a sense … without getting into the various types of “infinite” and “infinity” that are out there (to which whole books are devoted).

This inability to be expressed as a fraction – messy, endlessly rambling, chaotic – drove people nuts, starting way back in ancient Greece with the Divine Brotherhood of Pythagoras, who made a whole religion out of neat and orderly numbers. Unfortunately for naysayers, numbers like pi proved extremely useful, so everyone spent a couple of thousand years in the loop, bickering about how to define them. (They did, eventually.)

Transcendental numbers, to only crack the lid on this can of worms, are numbers that aren’t algebraic, which means – there’s no easy way around this – they aren’t the roots of polynomial equations with rational coefficients. Nobody proved pi was transcendental until 1882 – at which point people were still arguing about whether irrational numbers even existed.

So all the way from Pythagoras’ cult of bean-hating number-worshippers, past Newton and his apples, Leibniz and his monads, to the dawn of the 20th century, irrational numbers and their infinite series have been blowing people’s minds. Thus, some jolly nerds in San Francisco designated March 14 1988 the first official Pi Day, and the US House of Representatives, though famously logic-averse, even designated Pi Day a national event in 2009.

Irrational, messy, rambling pi turns out to be as American as apple … you know the rest.